To begin with, a mea culpa: In looking at the star spawn hulk in the previous post, I skipped over the Psychic Mirror feature. Mentally, I’d noted that it didn’t have any meaningful impact on the hulk’s own tactics—but having noted that to myself, I forgot to say so.
The thing is, Psychic Mirror doesn’t affect anything the hulk does, since the hulk already has another incentive to stand in the midst of its enemies, in the form of Reaping Arms. But Psychic Mirror can affect the behavior of other monsters fighting alongside the hulk. And when you get right down to it, “Psychic Mirror” is an inaccurate name: it should be “Psychic Amplifier,” because for every x points of psychic damage the hulk would take, every creature within 10 feet of it takes x points.
As an example, one commenter mentioned mind flayers, with their Mind Blast action. Suppose an attacking mind flayer blasts five player characters along with a star spawn hulk. First, each of the five player characters makes an Intelligence saving throw. On average, a PC will take 22 points of psychic damage on a failure, 11 on a success. But then the hulk makes its own saving throw, and its Intelligence is a wretched 7, so it has only a 20 percent chance of success—it’s going to fail, and take full damage, four times out of five. But it’s not the one who takes that damage! That damage is passed along to each PC within 10 feet of it—the full amount, even if a PC made his or her own saving throw!
Unfortunately for the hulk, while it passes the damage along, it doesn’t get to pass along its own debilitating condition, so in the likely event that it fails its save, it’s stunned by the Mind Blast and therefore can no longer make use of Reaping Arms. Thus, this may not always be the smartest play for the mind flayer—but one can imagine it working in particular situations.
Another commenter pointed out that two hulks within 10 feet of each other can theoretically reflect damage back and forth between them infinitely, straight-up killing any other creature in the radius. This is a frightening loophole that cries out for an erratum. In the meantime, Jeremy Crawford has apparently ruled that since multiple simultaneous uses of the same feature don’t stack, other creatures in range of Psychic Mirror don’t take the reflected damage more than once, although any additional hulk can cause the amplifying effect to reach farther.
I’m going to toss out one more glitch case, since it just occurred to me that there is a way in which it might conceivably affect the tactics of the star spawn hulk: Imagine that one star spawn hulk uses its Multiattack against a second star spawn hulk, and that the second star spawn hulk uses the Help action to allow itself to be hit, as a sort of anti-Dodge, granting advantage on the first one’s attacks. Thus, the second hulk takes 2d8 points of psychic damage, which is then broadcast outward to every other creature within 10 feet of either one of them. It’s weird and stupid, but according to RAW, it does seem to work.
Is it worthwhile, though? Only if Reaping Arms is on cooldown, and only if the damage is broadcast to seven or more enemies (the minimum necessary to exceed the damage that both hulks could do with separate Multiattacks), which isn’t likely ever to occur. If the second hulk Multiattacks as well, it only requires four enemies to receive the damage to begin to make sense, but all those enemies should have an armor class greater than or equal to the hulks’ AC 16. Otherwise, the hulks are trading away hit probability. They’re also physically hurting each other. So I say again, weird and stupid, and of negligible value.
OK, on to the star spawn seer, the lesser of the two boss-level star spawn. This one’s ability contour heavily favors Intelligence and Wisdom, with Constitution showing third. If it were a PC, this would be a typical contour for a support spellcaster, so we’re going to look for ways it can enhance the abilities of creatures (especially other star spawn) fighting alongside it. We can also examine it as a quasi-brute that uses its mental abilities, rather than Strength, to attack.
Like the star spawn hulk, it has proficiency in Dexterity and Wisdom saving throws, but not Constitution. Unlike the star spawn hulk, it doesn’t have quite a high enough Constitution for this not to be a weakness, or at least a drawback. In other words, spellcasters and other enemies whose powers require Constitution saves are among the things the seer considers meaningful threats. It’s immune to cold damage and to physical damage from nonmagical weapons.
Its Out-of-Phase Movement feature is similar to Incorporeal Movement, but unlike that feature, it does damage to other creatures it passes through, an effect that the seer can use offensively. It doesn’t do a lot of damage, but it does provide a small incentive to phase through opponents on purpose.
Jumping ahead to the Bend Space reaction, this seems like just a jerk move, like the goblin boss’s Redirect Attack feature. But the star spawn seer is very, very smart, and it won’t use this reaction just to avoid damage. Instead, it will look for ways to use it defensively and offensively at the same time. For instance, it can move to a location where it will be surrounded by enemies, bait out an attack—then use Bend Space to swap places with a star spawn hulk, which can then use Reaping Arms on its own turn. Or it can pick an enemy that would make a good target for a star spawn mangler but that the mangler can’t quite reach. Bait, swap, Flurry of Claws. Sure, Bend Space is useful as an escape hatch, but why just escape when you can also brutalize whomever you’re escaping from?
The star spawn seer’s big gun is Collapse Distance, which it will probably get to use only once in a typical combat encounter, since it recharges only on a roll of 6. For best effect, it should use Collapse Distance against a target that has at least two allies—the more, the better—within 10 feet of it, and it should also have someplace worth teleporting the target to, such as under a star spawn mangler or over a chasm. Finally, despite the feature’s very high DC, it’s still going to be less effective against high-Wisdom targets such as clerics, druids and rangers, so maybe aim it at someone else if possible? Then again, the presence of star spawn grues—whose Aura of Madness imposes disadvantage on all saving throws—can make this feature nearly impossible for anyone to resist.
Finally, there are the direct attacks: one melee, one ranged. Whatever the target’s evident preferred position, the star spawn seer will take the opposite. That is, against front-line fighters, paladins and barbarians, it will hang back and chuck Psychic Orbs. Against marksmen and spellslingers, if it can get to them, it will close and attack with its Comet Staff—two-handed, since it doesn’t carry a shield. Its speed is only 30 feet per turn, but if it’s accompanied by a fast-moving mangler, it can order its ally to charge the enemy, then Bend Space to swap positions with it.
Also, since the Orb is pure psychic damage—no accompanying physical damage to deliver it, as there is with the Comet Staff—the star spawn seer can lob one directly at a star spawn hulk that’s surrounded by enemies, and the hulk will rebroadcast the damage out in all directions and suffer no harm itself.
If the seer is seriously wounded (reduced to 61 hp or fewer), it will Dash away, using Out-of-Phase Movement, departing the scene by the most direct route, unobstructed by enemies, objects, walls or floors. (Not the ceiling—it has no flying speed. But you don’t have to be able to fly to fall.)
The star spawn larva mage is a legendary boss, the top of the star spawn pecking order. It’s also resistant to cold damage and to physical damage from normal weapons, and it’s also immune to a variety of debilitating conditions. Most notably, it can’t be paralyzed or restrained; if its foes want to stop it in its tracks, they’ll have to stun it.
The larva mage, like the star spawn seer, has a hybrid ability contour, with extraordinary Constitution and exceptional Intelligence and Strength; we can probably lump them together in the custom category “psychic brute.” The point being, the larva mage has little reason to hang back. Its abilities are mostly short-to-medium-range, an incentive to get into the midst of its enemies, within 20 feet of as many of them as possible (ideally, four or more).
Its list of actions may make it appear that it has two primary attacks, but it has three, the third being eldritch blast, which it can cast at will at up to three targets up to 120 feet away. (I’ll deal with circle of death in a moment.) Thus, if its opponents refuse to cooperate with its attempts to get next to as many of them as it can, it can still take potshots at them from a distance. Slam is a straightforward melee attack with the capacity to poison its target; note the 10-foot reach. Unless the larva mage is directly engaged in melee by an opponent, it may want to go ahead and cast eldritch blast against its target, since it can do more than three times as much damage this way; Slam is only useful in self-defense.
Plague of Worms is the larva mage’s big gun, its counterpart to the seer’s Collapse Distance, recharging only on a roll of 6. The larva mage wants to use this ability while standing within 10 feet of as many opponents as possible, because the effects are huge. So huge, in fact, that it almost doesn’t want to give its opponents a chance to get into position before using it—best-case scenario, it’s able to attack by surprise, drop right into the middle of the party and Plague away. It doesn’t have proficiency in Stealth or even particularly high Dexterity, so it probably won’t get this chance, alas. Still, if its opponents are anywhere near one another, this is the larva mage’s opening play, no question.
But what if they’re not particularly near one another? Dominate monster, which the larva mage can use three times per day, is an interesting option. For starters, thanks to its save DC and the fact that it can cast this spell three times a day rather than just once, it’s actually a better mind controller than the mind flayer. Sure, the obvious use of dominate monster is to make PCs attack one another. But for the larva mage, it can also be the “C’m’ere, you!” spell. The catch is, it can dominate only one opponent per action, so it may take some damage before it can get everyone rounded up and drop a Plague of Worms on them.
But it can take that damage, for a couple of reasons. First, lots of hit points and an out-of-this-world Constitution. Second, Feed on Weakness, which gives it 10 temporary hp every time a creature within 20 feet of it fails a saving throw. If it needs to top itself up a bit, it just falls back on a Slam attack and makes its opponent save versus poison. Feed on Weakness is also super-useful if the larva mage has hulks around forcing their own targets to make Con and Dex saves, even more so if there are grues to impose disadvantage on those saves.
The star spawn larva mage also has legendary actions, three per turn—although, mystifyingly, none of its choices costs any less than two of those actions, meaning it will never get to use more than one of them. Slam, by itself, offers very little for the cost, so the larva mage will use this choice only when it needs to defend itself and replenish its temporary hp at the same time. Feed is a good choice anytime one or more opponents are restrained by Plague of Worms and it’s evident that Slam won’t be necessary. Cantrip (read: “Cast eldritch blast again”) is the fallback if the larva mage won’t benefit from either Feed or Slam.
Unlike all the other star spawn, the larva mage doesn’t retreat when seriously wounded—it keeps fighting right down to 0 hp. This is because of its feature Return to Worms, which gives it limited immunity to dying. When the larva mage is reduced to 32 hp or fewer, it places itself within 60 feet of all its enemies and casts circle of death, with itself at ground zero. Even if it fails its own saving throw, it still has a two-thirds chance of surviving this spell, while each of its opponents takes an expected 21 points of necrotic damage. If it does happen to blow its save and take enough damage to reduce it to 0 hp, it merely turns into a swarm of insects. As a swarm, it doesn’t continue fighting, but rather Dashes away to safety, skittering up the nearest wall and fleeing across the ceiling. With any luck, it will escape while its opponents are nursing their wounds, giving it a chance to re-form the next day.